How to search Python dictionary for matching key?

When working with Python dictionaries, you often need to search for keys in different ways. You can search for exact keys or find keys that match certain patterns or contain substrings.

Searching for Exact Keys

If you have the exact key you want to find, you can use the [] operator or get() method to retrieve the value associated with this key ?

student_grades = {
    'alice': 85,
    'bob': 92,
    'charlie': 78
}

# Using [] operator
print(student_grades['alice'])

# Using get() method
print(student_grades.get('alice'))

85
85

Searching with Substring Matching

If you want to search for keys that contain a specific substring, you can iterate through the keys and use string methods like find() or in operator ?

Using find() Method

products = {
    'laptop_dell': 899,
    'laptop_hp': 750,
    'mouse_wireless': 25,
    'keyboard_mechanical': 120
}

for key in products.keys():
    if key.find('laptop') > -1:
        print(f"{key}: ${products[key]}")

laptop_dell: $899
laptop_hp: $750

Using 'in' Operator

products = {
    'laptop_dell': 899,
    'laptop_hp': 750,
    'mouse_wireless': 25,
    'keyboard_mechanical': 120
}

# More pythonic approach using 'in'
for key in products.keys():
    if 'laptop' in key:
        print(f"{key}: ${products[key]}")

laptop_dell: $899
laptop_hp: $750

Advanced Search Methods

Using List Comprehension

products = {
    'laptop_dell': 899,
    'laptop_hp': 750,
    'mouse_wireless': 25,
    'keyboard_mechanical': 120
}

# Find all keys containing 'key'
matching_items = {k: v for k, v in products.items() if 'key' in k}
print(matching_items)

{'keyboard_mechanical': 120}

Using Regular Expressions

import re

products = {
    'laptop_dell': 899,
    'laptop_hp': 750,
    'mouse_wireless': 25,
    'keyboard_mechanical': 120
}

# Find keys starting with 'laptop'
pattern = re.compile(r'^laptop')
matching_keys = [key for key in products.keys() if pattern.match(key)]
print(matching_keys)

['laptop_dell', 'laptop_hp']

Comparison

Conclusion

Use get() for safe exact key lookups and the in operator for substring searches. For complex pattern matching, regular expressions provide the most flexibility.